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Short Answers to Hard Questions About Clean Coal Technology

The Kemper County power plant in Mississippi.
Credit
Josh Haner/The New York Times

Technology holds the promise of enabling coal power plants, which produce much of the world’s electricity, to run more cleanly, emitting far less of the pollution that causes climate change. But these projects have been difficult to make a reality because they are complicated and expensive. Here is a quick primer.

​What is “clean coal”?

The term “clean coal” has been popularized by the coal industry, electric utilities and policy makers. It refers to the hopeful notion that technology will enable power plants to burn coal but release far less pollution. C.C.S., which stands for carbon capture and storage, or carbon capture and sequestration, is a type of clean coal technology that would prevent carbon dioxide (CO2) exhaust from entering the atmosphere from power plants that burn coal, natural gas and biomass, or other sources of carbon emissions like iron or steel factories and oil refineries. Since the early 2000s, there has been a wave of optimism that this technology could play a vital role in slowing climate change by cleaning up some of the biggest emitters of carbon pollution. Now there is significant skepticism that the technology can be scaled up affordably, reliably and soon enough to make a difference.

​Is C.C.S. necessary?

Most energy experts, including officials at the International Energy Agency, say that the technology is needed to slow climate change because it can significantly reduce carbon emissions from fossil fuels, which they predict will remain a large portion of the global energy mix through 2050. Many environmentalists, on the other hand, say that C.C.S. is a costly half-measure that delays the transition to renewable energy sources like wind and solar.

​How is the CO2 captured?

A power plant can trap carbon dioxide in one of three ways. After combustion, the carbon dioxide is captured from the exhaust of a power plant by absorbing it in a liquid, which is later heated to release the gas for storage. CO2 can also be captured before combustion. In this case, a controlled amount of oxygen is used to turn coal or natural gas into “syngas,” a mixture of carbon monoxide and hydrogen. Before it is burned to generate power, the syngas is treated with steam, producing carbon dioxide. A third method involves burning fossil fuels in oxygen. That results in an exhaust stream of water vapor and CO2, which are then separated by cooling and compressing the gas stream.

​What happens to the CO2 after it is captured?

The carbon dioxide is usually compressed and transported through a network of pipes for reuse or storage. It can then be stored by being injected directly into underground geological formations such as oil fields, gas fields, saline formations, coal seams that cannot be mined, and saline-filled basalt formations. It can also be compressed and shipped through a pipeline to an oil field, where it can be pumped underground in a process known as enhanced oil recovery, to help push up oil in a direction where it can be reached.

Will the Obama administration’s new limits on power plant emissions help promote C.C.S.?

Not likely. The Environmental Protection Agency has proposed a rule that in effect requires new coal-fired power plants to use carbon capture technology. Opponents of the rule maintain, however, that because C.C.S. is still so expensive, utilities will choose to provide energy from a different source like natural gas rather than invest in research and development of C.C.S. for coal-powered plants. They say that instead of advancing the technology, the rule will steer interest away from coal altogether, because it will become too costly to build coal plants. And with the current low price of natural gas, no one is building them anyway.

What steps has the administration taken to regulate power plant emissions?

As part of President Obama’s effort to tackle climate change, the E.P.A. is reining in carbon emissions from power plants, including all future coal and natural gas plants built in the United States. The agency has finalized two rules for power plants: one for new or modified power plants and another, the Clean Power Plan, for existing power plants. Though some states are moving forward with strategies to comply with the Clean Power Plan, it has been stalled by the Supreme Court pending the resolution of legal challenges.

​Will coal plants be able to satisfy the Obama regulations?

It won’t be easy. The limits on coal plants are stringent enough that utilities will probably be able to build new coal facilities only if the plants can capture about 40 percent of the carbon they produce.

​What is the biggest obstacle to C.C.S.?

Cost. The technology works. The economics don’t. Power plants with C.C.S. cost about 75 percent more than regular coal plants, and the infrastructure required to transport and store CO2 is enormous. It’s also essentially still free for plants to emit carbon dioxide into the air. Until there is a real cost to companies for emitting carbon unchecked, the financial case for C.C.S. will come up short.

​Why are C.C.S. plants so expensive?

Coal plants that capture carbon are expensive partly because they are so complex. As the New York Times reporter Henry Fountain explained, “removing carbon dioxide from the swirl of gases unleashed at a power plant is challenging, akin to plucking just a few colored Ping-Pong balls out of the air from a swarm of mostly white ones.” That price rises further because capturing and compressing the carbon requires so much energy, sometimes sapping more than 20 percent of the electricity that the plant is supposed to produce for consumers.

​Does fracking play a role in the economics of C.C.S.?

Yes. Fracking, a method of increasing production from drilled wells, has unlocked huge reserves of natural gas, which has driven down the price of natural gas to below $2 per unit. Generally speaking, natural gas prices need to be higher than $7 per unit for new coal plants to be competitive. This is a major reason no new coal plants are likely to be built in the United States anytime soon.

​Are there other costs to C.C.S.?

The technology generally eliminates only carbon pollution and does not remove other air toxins that cause asthma, lung disease, and heart attacks. It also does not reduce the environmental cost of mining methods like “mountaintop removal.” And if the captured carbon is used to foster more oil use, there are environmental costs to burning additional fossil fuels.

​Can the CO2 leak after it is stored underground?

Carbon dioxide injected underground could possibly escape, defeating the entire purpose of the carbon capture system. But the chances of that happening are extremely low, according to energy experts. The International Energy Agency says that depleted oil and gas fields are the most likely candidates for CO2 storage. These sites often contain multiple holes and wells built on these fields that create pathways for carbon dioxide to escape. The CO2 could taint drinking water or eventually rise to the surface and bubble into the atmosphere. In Cameroon, a volcanic lake suddenly released a cloud of naturally forming carbon dioxide in 1986, suffocating 1,700 people to death. If carbon dioxide is liquefied, injecting it deep underground can present problems, too. Pumping wastewater from oil and gas production into the ground has been linked to a series of small earthquakes in Arkansas, Ohio, Oklahoma and other states. Because of all this, long-term monitoring of storage sites will be required.

​The technology is proven, right?

Carbon capture and storage has been shown to work in many pilot projects, which generally do not operate at the scale envisioned by proponents as a solution to climate change. So the challenge is scaling it up to larger-capacity power plants. While there are some projects being designed or under construction, at least two power plants currently capture and stores carbon on a commercial scale. One is the SaskPower’s Boundary Dam 3 in Saskatchewan. The other is the Weyburn project, which gets its CO2 from a coal gasification plant in North Dakota and then sends it through a pipeline to the Weyburn oil fields in Saskatchewan for injection. But as The Times’s Ian Austen explained in March, Boundary Dam 3 has run into some problems. After initially saying that the project was working as intended, capturing 90 percent of the plant’s carbon, Cathy Sproule, a member of Saskatchewan’s Legislative Assembly, unveiled confidential documents in November 2015 indicating that the plant was working at only 45 percent of capacity. According to the Times article: “One memo, written a month after the government publicly boasted about the project, cited eight major problem areas. Fixing them, it said, could take a year and a half, and the memo warned that it was not immediately apparent how to resolve some problems.”

​How many C.C.S. projects are there?

There are 22 large-scale C.C.S. projects globally. Sixteen are operating. Four others, including the Kemper coal plant in Mississippi, are under construction; one is complete but awaiting a final permit; and one has been closed. Of all those projects, only four are coal plants. The rest are refineries, or natural gas, fertilizer, ethanol or steel plants. Only two of the four coal-based C.C.S. projects are operational: Boundary Dam 3 and Weyburn.

​If we give up on C.C.S., is slowing climate change still feasible?

Slowing climate change is possible without carbon capture and storage. Proponents, however, see it as vital to achieving carbon dioxide emissions reductions because countries will continue to rely upon fossil fuels like coal and oil as they take steps to slow climate change. In arguing that C.C.S. is the best solution, advocates point to forecasts showing that an energy scenario without it would make combating climate change much more expensive than with C.C.S. At the same time, C.C.S. has been slow to deploy, and many believe that even if the technology is scalable, it would come too late to reduce carbon emissions in a meaningful way compared with investments in renewables. Those who oppose C.C.S. insist that cost estimates for carrying it out are highly speculative.

​What would it look like for governments to commit fully to C.C.S.?

The chief executive of the Global CCS Institute, Brad Page, has said that to meet the target of keeping global temperature increases under 2 degrees Celsius, 130 full-scale carbon capture and storage projects will need to be operational by 2020. For C.C.S. to work on a national scale, the plants would also require a network of pipelines to transfer carbon. That network would have to be built in the next 30 to 40 years and be about 100 times the size of the current network, and be similar in size to what exists now for oil and natural gas. Deploying C.C.S. technology at this scale would require extensive and rapid government and private support.